The Study on Low-cost Position Sensor Using Index and Increment PWM

BLDC motors have the strong point of allowing high-efficiency operation, yet with the weak point of requiring position information for operation. Moreover, there have recently been frequent cases where the product differentiation of even a cheap BLDC motor demanded a high level of control performance similar to that of a controller using a high-precision position sensor. This paper proposes low cost position sensor that enables the acquisition of rotor position information based on index and incremental PWM, using a single position sensor instead of an expensive incremental encoder or a cheap 3 phase hall sensor. The characteristic of the proposed encoder is that index information at every 60° of electrical angle is inscribed on the encoder disk, as well as a multiple number of values representing information about PWM, which is obtained by modulating information about the electrical angle of the rotor that has the resolution of 60°. Such a method has the characteristic of enabling the acquisition of high-precision position information based on the information about a multiple number of PWM waveforms and counter values that have all been inscribed on the encoder disk for each 60° range. The feasibility of the proposed new encoder was verified by fabricating a prototype encoder generating 240 pulses, followed by confirming its performance using Micom’s capture and software counter functions.